Friends, definitely. I've tried really hard to like How I Met Your Mother, jumping into the DVDs several times over the years. I just don't enjoy it. The characters kind of annoy me, especially Alyson Hannigan who I am normally a huge fan of, and I didn't really laugh very much. I do like Barney though, he is the only thing that makes the show watchable for me, but one character does not a show make (excepting Mr. Ed).
Friends, on the other hand, I can rewatch all day long. The jokes are still really funny to me, not always in a laugh out loud sort of way but often some thought or concept will just be so damn amusing (for instance, Chandler's TV guide being delivered to "Chanandler Bong," it still makes me chuckle thinking about it now!). I also love all of the characters (okay, except for Phoebe), which makes a huge difference. I cared about seeing their lives unfold every week, and seeing the hilarious shenanigans they got into. I just can't say the same for HIMYM - there's no connection there, I just see actors trying too hard to be funny.